1. Field of the Disclosure
The disclosure is directed to bone screws with anchor features for securely attaching to low-quality cancellous bone, such as may be found, for example, in a vertebral body of a patient with osteoporosis.
2. Related Art
Pedicle screws are commonly used to attach a spinal fusion apparatus to a patient's spine. The screws are bored through cortical bone of the pedicle and place their distal portion in the cancellous bone of the vertebral body. The portion of the screw anchored in cancellous bone may be as much as 50%. The quality of the cancellous bone is therefore critical for the overall stability of the apparatus, as well as the success of the fusion process.
Several factors may reduce the quality of the cancellous bone. The patient's age is the most common factor. Diseases and injuries, such as, e.g., osteoporosis and vertical compression fractures, can further reduce the bone quality.
In patients with low-quality cancellous bone, the common solution is to fill the vertebral body with bone cement. This solution, however, may be inadequate due to extravasation of the bone cement. In addition, low-quality cortical bone on the outside of the vertebral body may not retain all of bone cement.
Accordingly, there is a need for pedicle screws that retain bone cement or provide alternative means of anchoring in low-quality bone.